(Let me examine him. Yes, the area is quite irritated. Tiny parasites exist, called pinworms, that produce these symptoms. Tonight, look at his anus closely, and bring the boy in the morning without washing the area.)

(Yes, let's see if we can see the eggs. In contrast to the adult worms, the eggs are too small to see with the naked eye, but with adhesive tape it is easy to collect them, to observe them with the microscope.)

(It's because these parasites deposit their eggs on the periphery of the anus during the night. I will prescribe him a chewable tablet that he will only have to take once. You must wash all of his clothes, including the sheets.)